Lithography is a fabrication technique that is employed for use in a number of industries, including the semiconductor processing industry. Specifically, photolithography uses an energy source such as ultraviolet (UV) light, x-ray wavelength, other wavelengths of radiation, etc. to expose selected regions of a surface. In one common technique, the surface includes a semiconductor wafer such as silicon that has been coated with a resist material. The resist material properties are locally changed when exposed to the energy source, which allows selected regions of the resist material to remain, while unwanted regions of the resist material are removed. In one method, the exposed regions of the resist are removed, in another method, the non-exposed regions of the resist material are removed.
In one method of photolithography, a pattern of features is created on a reticle, and the pattern on the reticle is focused onto a semiconductor surface using optics that adjust the scale of the pattern on the reticle to fit the semiconductor surface. In the semiconductor industry, there is an ever present pressure to reduce the size of features in the pattern to increase the density of patterned features packed into the same semiconductor surface area. In one example industry, manufacturers of random access memory chips such as dynamic random access memory (DRAM) strive to put more storage cells onto a chip.
As feature size decreases, photolithography of smaller and smaller features becomes more and more difficult. One problem that becomes increasingly significant, although still present on larger scales, is the optical interactions of the energy source, such as UV light or x-ray radiation. Because energy sources are wavelike in behaviour, constructive interference, destructive interference, and other optical interaction effects cause some reticle apertures to produce printed features that are not shaped as intended, or include unwanted features in addition to the desired features.
What is needed is a method and device that improves photolithography of small features and other features that produce unwanted results. Semiconductor manufacturing is also very commercially competitive. What is also needed is a method and device that reduces the manufacturing time and/or manufacturing cost.